In modern times the electrical energy storages are becoming an integral part of the distribution grids, ensuring the on-demand and reliable supply of electricity by the intermittent renewable energy sources (wind, solar) and providing a stable and efficient operation of the base-load fossil-fuel-fired and nuclear power plants around the clock.
Amongst the known methods for energy storage able to accumulate a lot of excessive energy and store it over a long time-period, the recently proposed methods for Liquid Air Energy Storage (LAES) (see e.c. Patent FR 2,489,411, US patent Application 2012/0216520 and WO Patent Application 2015/138817) are distinguished by a much simpler permitting process and the freedom from any geographical, land and environmental constraints, inherent in other known methods for large-scale energy storage technologies, like Pumped Hydro Electric Storage (PHES) and Compressed Air Energy Storage (CAES). In the LAES systems liquid air is produced using excessive power directly from the renewable energy sources or from the grid, stored in the small volume tanks between the off-peak and on-peak hours and pumped, re-gasified and expanded with production of a peaking power in the periods of high power demand. However, producing a liquid air during off-peak hours is an energy intensive process and many technical solutions have been proposed to reduce the energy consumption during LAES charge, increase the energy release during LAES discharge and in this manner to improve the LAES round-trip efficiency.
One of the possible ways for increase in energy release during LAES discharge could be its co-location with the power plant existing or planned to be constructed and recovery a waste heat of power plant exhaust for increase in temperature of discharged air prior to and in the process of its expansion (see e.c. US Patent Applications 2009/282840). However this possibility may be realized only with the availability of such co-located power plant and at its exhaust temperature high enough for waste heat to recover. The another proposed method for augmentation of the LAES output power consists in use of discharged air as combustion air at the co-located gas turbine plant (see e.c. WO Patent Application 2014/000882). The latter method seems to be the least substantiated by reason of excessively high specific air consumption typical for the gas turbine prime mover. This air consumption exceeds that typical for the comparable in power reciprocating internal combustion engine by a factor 2-3, resulting in the attendant increase in charging power and a required volume of liquid air tank at the LAES facility.
Because of this the method for fueled augmentation of the discharged power of the LAES facility with use of a supercharged reciprocating engine is proposed in the published U.S. Patent Application No. 2018/0221807. This makes possible not only to increase the LAES discharge power by more than 45%, but to gain also the additional benefits, resulting from a simple and efficient recovery of engine exhaust energy.
This technical solution provides also zero carbon emitting LAES facility exhaust through recovering the cold thermal energy of discharged liquid air being regasified for cryogenic cooling the facility exhaust with capture and removal of all CO2 emissions from the said exhaust. However, even without any cryogenic exhaust treatment, the principles built into design and operation of any LAES facility already in themselves provide a very low level of CO2 emissions in engine exhaust, which is, for example, a half of upper limit on carbon emissions from the large stationary CC gas turbine power plants set up by the new U.S. Carbon Pollution Standard in 2015. This circumstance weakens a motivation of the end-users on harnessing the proposed method for cleaning the LAES facility exhaust. In addition, despite the general public concern by the problems of global warming, at the present time there are not a substantial active world CO2 market and the much accessible ways for CO2 sequestration, This creates the problems for the marketing the CO2 produced. Therefore there is a need for such improvements in the discussed method, which could remedy its market entry problems of today through creation of an alternative way for internal using the most part of CO2 cryogenically produced instead of its marketing or sequestration.
The basis for this alternative way is a finding, according to which the cold thermal energy of liquid air being regasified in the LAES system may be used for a partial cryogenic capture of CO2 emissions at a rate much exceeding the rate of their formation in the fueled reciprocating engine. This opens up possibilities for recirculation of a captured part of CO2 emissions to the engine inlet in mixture with the discharged regasified air and thus creation of the semi-closed CO2 bottoming cycle. From operation of the LAES system with this bottoming cycle the following benefits may be gained: a) further increase in the LAES discharged power output, which is an initial goal of the basic invention being now improved; b) the said increase in power without use of an additional equipment, resulting in a marked decrease in the CAPEX of LAES facility; and c) a significant decrease in NOx emissions level at LAES facility exhaust, resulting from suppression of thermal NOx formation in the process of fuel combustion in the engine cylinders. The latter is achieved through replacement of a part of oxygen at the engine inlet by recirculating CO2 component, having much higher heat capacity and thus reducing a gas temperature level in the engine cylinders. The impact of a proposed CO2 recirculation on suppression of NOx formation is comparable to the impact of well-known exhaust gas recirculation (EGR), but the practical implementation of CO2 recirculation is much simpler and cheaper.
By this means, the method for liquid air energy storage including its fueled power output augmentation with cryogenic treatment of the LAES facility exhaust is selected as a subject for the innovative improvements in the present invention. Thereby, a cryogenic capturing a part of CO2 emissions and its use for further facility power augmentation and reduction in NOx emissions are found to be the proper ways for achievement of the invention's goals.